It will be better and much cheaper to find the disc.
You will either need a machine specific, gray disc that shipped with the machine, or, a retail version of Leopard.
Machine specific discs are iffy at best, unless you happen to have a record of the disc version that you had.
Retail discs are available on eBay, but are costly.
Let's try and reset your main password without a disc. Follow these instructions:
Another take with other options:
You can call Apple Customer Support 1-800-767-2775, provide the Serial Number and specifications of the Mac, and for a fee, a replacement set of system discs (if available), can be ordered.
However, the discs will be for the original version of OS, that was pre-installed, when the Mac was manufactured.